Deadly Songbird Parasite Evolving Rapidly

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The bacteria responsible for the red, swollen, crusty eyes of a
sick house finch, which can leave it unable to survive, evolve at
an exceptionally fast rate — which is both bad and good news for
the future of the songbird, researchers say.

The fast evolution means the bacteria can keep up with their
hosts' immune systems. However, in the process of evolving, the
bacteria have lost genes that may protect them from viruses.
That's a weakness scientists could take advantage of to get rid
of the bacteria, which have led to the
death of thousands of house finches in the wild since the
bacteria jumped species and started an epidemic in the 1990s.

Bird bacteria

The tiny bacteria, Mycoplasma gallisepticum, infected
poultry before it adapted to the house finch population. The
researchers analyzed several samples of the bacteria from
different years of the epidemic (the mid-1990s, 2001 and 2007)
and compared them with strains isolated from chickens and
turkeys. They were able to determine that the bacteria likely
jumped from the turkey population, a possibility that other
researchers had suggested. [ 10
Deadly Diseases That Hopped Across Species ]

By analyzing genetic sequences, researchers discovered that the
bacteria mutated 10 to 100 times more quickly than other species
of bacteria, seemingly giving them an evolutionary advantage.

"We were surprised at what a high rate it was; it's higher than
most published estimates and on par with just a few estimates out
there," study researcher Scott Edwards, of Harvard University,
told LiveScience.

That wasn't all that was hiding in the bacteria's genome,
however: "We were surprised to find that the bacteria's own
immune system against viruses and phage was evolving," Edwards
said. "The bacteria lost about 50,000 base
pairs [of DNA ]; as a result of this, it loses some functions
that were formerly advantageous" — such as its ability to fight
off viruses.

The researchers said they aren't sure whether the loss of key
immune-system genes was an artifact from the bacteria's move to
the new host (perhaps the small population of bacteria that
started the epidemic had already lost their immunity genes) or
whether they lost them along the way because it somehow gave them
an advantage in the house finches.

A bacterium's immune system defends against viruses called phage.
Without the immunity, a virus could attack unimpeded and kill the
bacterium. Researchers say the mycoplasma may
no longer be able to fight off pha ge, though the researchers
don't know enough about such viruses to really say what would
make a good weapon.

"Who knows, maybe we could
enlist some viruses to get rid of them," Edwards said.
"That's one of the next things we want to do, look at how this
loss of the immune system in the bacteria affected its
susceptibility to phage."

The study was published today (Feb. 9) in the journal PLoS
Genetics.

You can follow LiveScience staff writer Jennifer Welsh on
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